Two large parallel gray surfaces with emissivities of 0.9 and 0.8 are maintained at 90°C and 25°C respectively. The space between the plates is evacuated. (a) Calculate net rate of radiation heat...

Two large parallel gray surfaces with emissivities of 0.9 and 0.8 are maintained at 90°C and 25°C respectively. The space between the plates is evacuated. (a) Calculate net rate of radiation heat transfer between the surfaces. (b) A thin meal radiation shield with gray surfaces of emissivity 0.3 is placed between the two plates. Calculate (i) the temperature of the shield and (ii) the external heat input to the two plates.